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Old 04-28-2018, 05:04 AM   #1
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Exclamation ST34 2011 odour issue

We own a ST34 2011 which we bought late 2016. We absolutely love it but we do occationally experience a slight odour problem related to the head / holding tank setup. I have checked everything for leaks but it all seems to be in good order. Also if it was a leak I assume it would most likely smell bad all the time. The problem is not directly related to how full the tank is either so a bit at loss here🤔

My question is if anybody have had similar issues and can recommend a solution? I have checked the owners manual to see if there is a holding tank ventilation tube installed which might have an active carbon filter that I can try to replace but it doesn’t seem like there is??

Any advice would be much appreciated

Greeting from Denmark
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Old 04-28-2018, 05:28 AM   #2
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Peggie Hall is the expert on this subject and hopefully she will chime in, but for now here are a couple of suggestions to try:

The head hose may be the problem. After a while the insides permeate the hose and coat the outside of the hose. So take a wet paper towel, wipe down a section of the hose and then smell it. Any bad smell and your hose has permeated. Sealand makes low permeating replacement hose.

The holding tank requires a vent and I am sure that Beneteau installed one. But it may be kinked, plugged or just maybe too small. Trace it out, make sure a mud dauber hasn't built a next in the outside vent. Also make sure that it continuously slopes upward.

If ok then replace the vent hose with one size larger. You need sufficient fresh air interchange with the holding tank to make it aerobic rather than anerobic which causes the odors.

At the very last after all of the above has been exhausted then consider a charcoal vent filter. But that is a kludge and a proper vent wont stink.

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Old 04-29-2018, 04:37 AM   #3
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Hi David

Thanks for a quick reply. I will try to track down the vent hose which must be there, my hope was that somebody knew where ��

I’ll also try to wipe down the hoses and check for smell, can the hoses actually be permeated after just 7 years?

Thx Kim
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Old 04-29-2018, 06:44 AM   #4
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Yes, it all depends on the quality of the hoses used originally.

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Old 04-29-2018, 06:50 AM   #5
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What holding tank treatment products are you using? Fresh or salt water flush? I second a read of Peggy Hall's book for hints and cures.
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Old 04-29-2018, 09:21 AM   #6
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I know you said head holding tank, but when I had odor issues on our Beneteau it turned out to be the shower condensate trap. We rarely used the shower, so I never checked it. Opened it, and it had some nasty slimy water inside. Mucked it out and wiped it with bleach. That sensor “whale” failed and the condensate pump was running non stop which was the reason I went in there. May be worth checking if you have not already done so.
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Old 04-29-2018, 10:03 AM   #7
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Unless a tank is leaking, it's rarely if ever the source of odor INSIDE a boat because odor from inside the boat has only one place to go--out the vent. If the odor is only occasional, it MIGHT just be odor out the vent coming into the boat via an open hatch.

David, I think you need to read the part of my book that deals with holding tanks and vents again...A blocked vent would not create odor in the boat, it would pressurize the system...leading to one of several catastrophes, the least of which would be an eruption back through the toilet or a geyser when you open the deck pumpout cap...the worst of which can be a burst tank.

The three most common sources of odor on a boat are permeated sanitation hoses (7 years is a very long time for the sanitation hoses used by most builders...the least expensive hoses--single wall flexible PVC--can permeate in a matter of months), wet dirty bilges and sumps.

Odors are strongest at their source, so stick your nose into enclosed places immediately upon coming back to the boat--before you open it up and air it out.

There's more, but I'm about to be late for church...I'll be back later. Meanwhile, I appreciate the plugs for my book...it's available in both kindle and print from Amazon (see link in my signature).

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Old 04-29-2018, 10:37 AM   #8
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Thanks for all the helpfull replies everybody, there are a lot of good inputs about what to check out. Not the least it sounds like I need to get on Amazon and buy Peggie’s book😉

The shower condensate trap could actually also be the source. We’ve never used the shower but maybe the previous owner did. Definitely worth checking out.

I’ll stick my nose deeper into this so to speak and see if I can get a clearer identification of the source.

Thx, Kim
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Old 04-29-2018, 10:50 AM   #9
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One more thing, the holding tank should have a vent filter, but mine didn't. I am 100% sure of this and traced it every inch of the outlet line. Every time someone flushed the head, I got a shot of the odor on the aft end of the boat. I looked at installing one, but the required geometry was not available to put one in.
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Old 04-29-2018, 10:53 AM   #10
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Sunchaser,

We’re using using A product from Thetford (the green bottle version I forget the exact name) and it is a seawater flushing electric head from Jabsco.

Thx, Kim
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Old 04-29-2018, 10:59 AM   #11
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Fletcher500,

Thinking more about it we do actually experience the problem most often when flushing. I will definitely trace the vent tube and see what state that is in and if it has a filter.

Thx Kim
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Old 04-29-2018, 11:21 AM   #12
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I have noticed sometimes when the wind is just right (or wrong) and the aft cockpit doors are open, I can get the "station wagon effect" with outside fumes coming in, either exhaust or head vent smells. Closing the door(s) resolves the issue.

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Old 04-29-2018, 01:20 PM   #13
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Quote:
Originally Posted by Niceneasy View Post
Sunchaser,

We’re using using A product from Thetford (the green bottle version I forget the exact name) and it is a seawater flushing electric head from Jabsco.

Thx, Kim
Kim

Converting seawater flushing to fresh water is well worth considering for odor control.
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Old 04-29-2018, 02:15 PM   #14
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Quote:
Originally Posted by Niceneasy View Post
Thanks for all the helpfull replies everybody, there are a lot of good inputs about what to check out. Not the least it sounds like I need to get on Amazon and buy Peggie’s book

While you are buying the book, buy the Kindle edition as well. I think it is really inexpensive when purchased with the book and it means that you can always reference it, whether on the boat or at home.
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Old 04-29-2018, 04:07 PM   #15
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One more thing, the holding tank should have a vent filter...

No, it shouldn't except as a last resort. Vent filters actually help to cause the very problem they're sold to solve (why couldn't I have invented something that does that???) because they impede the flow of fresh air needed to PREVENT odor.

Sewage—all organic material--contains both aerobic (needs oxygen) and anaerobic bacteria (functions in the absence of oxygen); but only the anaerobic bacteria produce foul-smelling, and also highly toxic, gasses--sulfur dioxide, hydrogen sulfide--and also methane, which is odorless. But when organic matter breaks down aerobically, it converts to CO2, which is an odorless gas, and water. So, as long as there is a sufficient supply of oxygen to the tank, and an aerobic treatment is added to aid that which naturally occurs in sewage, the aerobic bacteria thrive and overpower the anaerobic bacteria, and the system cannot produce odor. Filters make it impossible to create an aerobic environment in the tank.

A larger diameter vent line that's short, straight an relatively horizontal is usually enough to provide the oxygen needed...but even when that's not possible, the answer isn't a filter...aeration is.

Chemical tank products don't help because they kill the bacteria needed to break down waste. Thetford tank treatments are all highly toxic chemicals--formaldehyde, gluteraldehyde or quaternary ammonium compound. OdoBan from Walmart is another highly toxic product. To maintain a tank aerobically requires products that work WITH nature instead of against it. There are several on the market...No-Flex Digester, Odorlos, Raritan K.O. are the most well known.

That's the short version....the long version is in my book.

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Old 04-29-2018, 05:11 PM   #16
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What the Headmistress said Get her book and all will be good
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Old 04-29-2018, 05:29 PM   #17
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Will do, will do ;o)
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Old 04-29-2018, 05:33 PM   #18
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We had a boat that had an 80 gallon holding tank. It got really bad smelling whenever a toilet was flushed and air displaced from the holding tank. After talking to Peggie we installed a Groco Sweetank. It pumps air into the bottom of the holding tank so air would bubble up through the sewage. As soon as I turned it on the smell outside the boat was horrible for 2 hours and then the smell went away. We owned the boat for 8 years more and never added any chemicals into the holding tank. No smell ever. Do not put a filter on the vent as Peggie says. If possible add a second vent to the other side of the boat to allow air to flow through the tank.
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Old 04-29-2018, 06:06 PM   #19
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Thanks for setting me straight re the vent Peggie. Good info.
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Old 04-29-2018, 06:24 PM   #20
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In a similar vein, my toilet is surrounded on three sides by plywood, and I expect that, the boat being 35 years old, urine spray may be responsible for the pee pee smell. Any guy peeing with bare legs will tell you it might be a contributor...

Yet no amount of cleansing of the walls, even after replacing the pump/macerator with the associated cleanup for that made any difference.

A dog expert (OK my daughter) said to get some pet pee enzymes from a pet store, and wash the area with that.

Will do, but does anybody recognize this approach?
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